Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $92.87   3.283%   $95.9189   $95.92   $95.90   $95.90  
  Purchase #2 $105.94   13.471%   $120.2112   $120.21   $120.20   $120.20  
  Purchase #3 $137.42   12.443%   $154.5192   $154.52   $154.50   $154.50  
  Purchase #4 $166.59   12.734%   $187.8036   $187.80   $187.80   $187.80  
  Purchase #5 $52.54   8.433%   $56.9707   $56.97   $56.95   $57.00  
  Purchase #6 $167.28   11.311%   $186.201   $186.20   $186.20   $186.20  
  Purchase #7 $214.52   3.649%   $222.3478   $222.35   $222.35   $222.30  
  7 purchase totals = $937.16       $1,023.9724   $1,023.97   $1,023.90   $1,023.90